Arthur's heard rumours, whispered in the dark corners of Camelot where Uther's law is yet to tread, of the bond of true love stitching a pattern of your lover's wounds on your body. He hadn't dared believe them. He hadn't hoped until Merlin nicked his finger slicing an apple for Arthur one day and on Arthur's thumb bloomed a fiery red line. Then he had rejoiced.

In which the only reason Arthur and Merlin kiss is to boost Arthur's luck, of course.